Quantification of exercise training dose in phase III cardiac rehabilitation: A UK perspective

Abstract

General Abstract The Apple watch was a new technology first introduced in 2015. At that time, its validity and reliability for measuring stepping frequency and heart rate monitoring during exercise was unknown. Current evidence indicates that the effectiveness of cardiac rehabilitation (CR) programmes for improving patient outcomes may be questionable in the United Kingdom (UK). We postulated that the exercise dose that patients receive during Phase III CR may not be a high enough stimulus to invoke a positive physiological adaptation. Therefore, this thesis aims to examine the validity and reliability of the Apple watch for measuring heart rate and step frequency. We then planned, based on our initial findings, to apply this technology to patients undertaking Phase III CR in order to monitor and quantify exercise dose and training progression to determine the fidelity of the intervention.

The aim of the first study was to examine the validity and variability of the Apple watch for measuring step count. On two occasions, 21 males completed treadmill exercise while wearing two Apple watches (left and right wrists) and an ActivPAL (criterion). Exercise involved 5 min bouts of walking, jogging, and running at speeds of 4 km.h-1, 7 km.h-1, and 10 km.h-1, followed by 11 min of rest between each bout. There was a small under-estimation in step count during walking but large and very large over-estimations during jogging and running. There were poor to very poor correlations during walking, jogging and running. The inter-device variability showed good to nearly perfect intraclass correlations and small to moderate standardised typical errors. Intra-device variability was large to very large for all exercise intensities. The Apple watch has adequate validity for measuring step count during walking, but very poor validity during jogging and running. On this basis, we concluded that quantifying stepping frequency during Phase III CR using the Apple watch should not be pursued.

The aim of the second study was to examine the validity and reliability of the Apple watch heart rate sensor during and in recovery from exercise. Twenty-one males completed treadmill exercise while wearing two Apple watches (left and right wrists) and a Polar S810i monitor (criterion). Exercise involved 5 min bouts of walking, jogging, and running at speeds of 4 km.h-1, 7 km.h-1, and 10 km.h-1, followed by 11 min of rest between bouts. At all exercise intensities the mean bias was trivial. There were very good correlations with the criterion during walking (L: r = 0.97; R: r = 0.97), and good (L: r = 0.93; R: r = 0.92) but poor/good (L: r = 0.81; R: r = 0.86) correlations during jogging and running. Standardised typical error of the estimate was small, moderate, and moderate to large. There were good correlations following walking, but poor correlations following jogging and running. The percentage of heart rates recorded reduced with increasing intensity but increased over time. Intra-device standardised typical errors decreased with intensity. Inter-device standardised typical errors were small to moderate with very good to nearly perfect intraclass correlations. The Apple watch heart rate sensor has very good validity during walking but validity decreases with increasing intensity. On this basis, we chose to introduce the Apple watch to a Phase III CR programme for monitoring individual exercise dose via heart rate.

The aim of the third study was to investigate the fidelity of a structured Phase III cardiac rehabilitation (CR) programme in the United Kingdom (UK), by monitoring and quantifying exercise training intensity. We compared the mean % heart rate reserve (%HRR) achieved during the cardiovascular training component (%HRR-CV) of a circuit-based programme, with the %HRR during the active recovery phases (%HRR-AR) in a randomly selected cohort